LED device that has advantages of low power consumption, less heat generation, long life, small size, impact tolerance, high speed, free mercury and good optical performance has been applied to provided an optical device light source with steady waive length or been applied as an indicator of an electronic device. The brightness and operation life of a LED device has been tremendously improved along with the development of the optical technology, and may serve as the primary light source of an electronic device in the future.
For example, a LED device is available to a thinned liquid crystal display (LCD) in compliance with the design trend to downsize.
FIG. 1 partially illustrates a cross section view of a prior back light module 100 applied in a LCD with a LED device as a light source. The back light module 100 comprises a light guide plate 104 and at least one LED device 101 coupling with the light guide plate 104. The LED device 101 having a die 109 is fixed and electrically connected to a control circuit board 106 via a lead 102, wherein the control circuit board 106 is set on a rear plate 103 of the back light module 100. Light emitting from the die 109 of the LED device 101 either is diffused directly by the light guide plate 104 and or reflected by the reflector 105 prior to the diffusion of the light guide plate 106. The diffused light is then emitted out of the back light module 100 to provide the LCD with a well-mixed plane light source.
In general the lead 102 of the LED device 101 is fixed on the control circuit board 106 by a surface mounting technology. As shown in FIG. 1, when the LED device 101 is thick enough a rear lead design is applied, wherein the lead 102 set on the rear side of the LED device 101 can be securely mounted on the control circuit board 106 that is perpendicular with the light emitting direction R1 of the LED device 101.
However, since a light guide plate is a primary element of a LCD, when a thinner LCD is required the light guide plate should be thinned as well. Thus a decreased thickness of the LED coupled with the light guide plate may also be required. In that case, the lead 102 set on the rear side of the LED device 101 has smaller contact area to mount on the control circuit board 106. The lead 102 may not be secured on the control circuit board 106 firmly, and heat generated by the LED device 101 may not be dissipated effectively due to the smaller contact area. The manufacture yield of the LCD may be decreased.
To resolve these problems, a lateral lead design is then adopted. FIG. 2 partially illustrates a cross section view of another prior back light module 200 applied in a LCD. The lateral lead design applies lead 202 set on the lateral side of LED device 201 and mounted on the control circuit board 206 that is parallel with the light emitting direction R2 of the LED device 201.
However the lateral lead design still does not resolve the problems of heat dissipating due to the decreased contact area between the lead 202 and the control circuit board 206. Because the metal structure of the lead 202 of the lateral lead design may be partially torn by undue fold compared with the lead 102 adopted by the rear lead design. The lead 201 with undue fold may obstruct the primary heat dissipation of the LED device 201 and affect the optical performance of the LED device 201.